Thats weird if its not the coins changing. What could be the problem? When it happens, its for 5-10 seconds each time.
I am using MultiMiner to monitor my rigs which are in another network and although I have a back up pool, it doesnt report as the eu pool being down. So it does not change pool.
I think you have a power issue, the GPU load is unaffected by coin switching. Do you have a kill-a-watt? I would check exactly how much power you are pulling from each of your PSUs, you might be overloading them. Also what is the max AMP of your circuit you are running, 5 rigs on? (you said 5 right?) I had a 50amp circuit wired just for my rigs that run around 2000 watts.
On another note, the amount of rejected is nuts with this pool, I get a lot of 'rejected untracked stratum shares' which I have never seen before. The bottom screen with the pretty colors is 1 of my many gridseeds, you can see even that is running at almost a 10% loss of shares.
You have to look at the rejected shares beside your individual cards; ignore the overall rejected shares at the top of the miner. There is some bug somewhere causing it, but they are not actually rejected.
I have mined here a few days and I can say that the mh/s listed at the top of the website is about 95%-100% accurate. Use your accepted hash rate and multiply by the advertised mh/s.